Such a generator is intended to be used in applications in which it is necessary to transmit high-power short (on the order of a nanosecond or above) electrical pulses (several kilovolts). It is also important that it be capable of being synchronized with other electrical or optical systems. The prior art comprises purely electronic pulse generators. These generators make it possible to produce high-power electrical pulses lasting between several picoseconds and several milliseconds. Nevertheless, these generators are not capable of being perfectly synchronized with one another and also do not enable the spectral content of the output pulse to be controlled.
To obtain high-power short electrical pulses—typically on the order of the nanosecond or above—it is known to use optoelectronic switching generators, called frozen wave generators. These generators use various semiconductor substrates. A number of switching modes are known, including a so-called “avalanche” mode and a so-called “linear” mode.
A generator using an avalanche switching system is described in the patent document U.S. Pat. No. 4,782,222. This generator includes a semiconductor substrate block, two conductive elements coupled to said block and separated by a determined distance, a high-voltage power supply arranged between the two conductive elements as well as means for illuminating said block at a given wavelength so that most of the light penetrates said block over a distance below the distance between said two conductive elements. Such a system makes it possible to perform very high-voltage switching while requiring little optical energy.
The photoconductor systems operating in an avalanche mode nevertheless have a certain number of disadvantages, including a significant time jitter (on the order of several tens of picoseconds) for synchronizing short pulses—nanoseconds or sub-nanoseconds. This time jitter associated with optoelectronic switching limits the possibilities of perfectly controlling the time and therefore spectral profile of the electrical signal produced. This results in poor reproducibility of the short photogenerated pulses.
A linear generator is described in the publication WO 2007/074229. This generator includes means for storing electrical charges, a high-voltage source capable of charging said charge storage means. It also includes two passive doped-silicon photoconductive elements operating in a linear mode forming photosensitive switches, the first being connected to the reference potential and to storage means, and the second being connected to the storage means and to an effective charge. It finally includes a first light source capable of delivering a light pulse to said first photoconductor, a second light source capable of delivering a light pulse to said second photoconductor, as well as means for synchronizing the transmission delay between the first and the second light source.
Such a generator makes it possible to provide electrical pulses of peak-to-peak amplitude of several kilovolts for a sub-nanosecond duration of the bipolar signal. In addition, the time jitter is made very low—on the order of a picosecond—thereby making it possible to finely control the profile of the spectrum of the signal delivered. Finally, this generator enables high reproducibility of the source and has a very long lifetime.
However, a linear optoelectronic generator has a number of disadvantages. In particular, the control of the spectral content of the pulse by adjusting the time delay between the two photosensitive switches does not allow for sufficient control of said content. Moreover, the means for adjusting the time delay between the two photoswitches integrates a delay line, thereby making the system bulky. Such a generator cannot be synchronized with other electrical or optical systems. Finally, the linear mode requires a large amount of optical energy and therefore the use of bulky laser sources. Thus, there is no solution in the prior art that would make it possible to obtain a low-profile electrical pulse generator capable of being synchronized with other electrical or optical systems, with high-power (several kilovolts), short (nanosecond and below) pulses and with controllable spectral content.